The preferred embodiment concerns a system and a method to detect a fire in a fixer unit of an electrographic image generation device. It is known to arrange a smoke sensor in a suction channel through which the exhaust is drawn from a fixer space of a fixer unit.
From the document DE 102 15 353 A1 it is known to arrange a sensor arrangement with electrically conductive sensor cables below a substrate material to be fixed, which sensor cables burn through upon meeting a burning portion of the substrate material. In the event of a fire, the current flow through the burned-through sensor part is interrupted and an error signal is generated.
In particular in radiation fixer units with radiation heating elements, a risk of fire exists due to substrate material residues that are exposed to the radiant heat generated by the radiation heating elements. The possibility also exists that, given an unexpected stoppage of the substrate material, the heat power of the radiation heating elements cannot be reduced quickly enough, whereby the substrate material exposed to the radiant heat can be ignited. In particular in high-capacity printers with printing speeds of ≧1 m per second, a high heat power of the radiation fixer unit is required in order to provide the energy required for fixing. Infrared heat radiators below or-between which a substrate material with a toner image to be fixed on the substrate material is directed are advantageously used in the radiation fixer unit. This toner image is fixed on the substrate material via the heat radiated by the heat radiators. The infrared heat radiators thereby generate a temperature of multiple 100° C. Stopped paper in the region of the heat radiators ignites in the shortest time, i.e. within a few seconds.
In order to be able to better control the heat power of the heat radiators and to protect the substrate material to be fixed from the unwanted heat radiation, the heat radiator can be temporarily covered with a blind arrangement. Such a blind arrangement is known from the documents DE 198 27 210 C1 and DE 103 38 516 B3, for example. The use of a blind is in particular advantageous when a paper web should be printed and toner images located thereupon should be fixed. Upon opening this blind, paper residues located in the radiation region of the heat radiators (which paper residues have remained in the fixer unit after a tear of a paper web to be printed, for example) can be ignited. The fire of the paper residues typically propagates in the fixer unit and spreads to the paper web. The occurrence of a fire in the fixer unit must be detected as quickly as possible in order to be able to take measures via which a propagation of the fire is prevented.
As mentioned above, various sensor arrangements are known to determine a fire in the fixer unit. After the fire detection, the fire area (i.e. the fixer region of the fixer station) can be sealed off. Partitions are advantageously used for this, wherein a first partition is arranged before the fixer unit in the main transport direction of the substrate material and a second partition is arranged after the fixer unit in the main transport direction of the substrate material. Upon detection of a fire in the fixer unit, these partitions are closed, whereby the fire area is hermetically sealed. The burning paper residues as well as the paper web burn at maximum up to these partitions. After a cleaning of the inside of the fixer unit, the printing operation can be continued.
One possibility for fire detection of the fixer unit is to monitor an exhaust air flow (generated from the fixer unit with the aid of a suction device) with the aid of a smoke sensor. A portion of the primary air flow can thereby be diverted and directed via a filter element to the smoke sensor. Its output voltage increases proportional to the particle flow present in the exhaust current monitored by the smoke sensor. If the output voltage exceeds a preset limit value, the sensor detects a fire in the fixer unit and the partitions are closed. Due to the complex current relationships and various possible fire locations, a significant time (in particular multiple seconds) can elapse between the start of a fire and the fire detection, whereby necessary safety reactions are unnecessarily delayed.
Furthermore, it is not possible to differentiate smoke particles from other particles contained in the exhaust flow with the aid of smoke sensors, whereby a fire can also be detected by the smoke sensor when, for example, many particles generated by contaminants are contained in the exhaust due to a significant friction of the substrate material, which particles cloud the exhaust. Faulty activations can thereby occur due to these contaminants. Such contaminants can in particular arise due to paper dust particles, toner particles or due to emissions from offset printing methods. A quick, correct detection of a fire is thus possible only with difficulty in the prior art, wherein faulty activations cannot be safely avoided.
The cited documents are herewith incorporated by reference into the present specification. In particular, the constructive and functional design of the radiation fixer units described in these documents as well as the blind shielding of the radiation fixer units can advantageously be used in connection with the embodiment described in the following.
A device to monitor a region in a fixer unit for smoke development is known from the document DE 2148901 A, in which a single light source serves as a light source for fixing the toner material adhering on a substrate material and as a light source for a sensor arrangement to detect smoke.
An arrangement for certain controlling of a fixer unit during a stoppage of the substrate material is known from the document JP 60133487 A, in which the temperature of the substrate material to be fixed is detected. A conflagration of the substrate material should thereby be prevented.
An automatic fire suppression device for use in an electrophotographic copier in order to extinguish a combustion of a flammable substrate material in the fixer unit is known from the document U.S. Pat. No. 3,753,466 A. Means to detect a fire are thereby provided.
It is an object of the invention to specify a method for detection of a fire in a fixer unit of an electrographic image generation device and a fixer unit with a device to detect a fire, via which a fire can be quickly and accurately detected.
In a fixer unit system and method to detect a fire in a fixer unit of an electrographic image generation device, at least one portion of a fixer region of the fixing unit is monitored with a photoelectric sensor arranged adjacent to a substrate material having a toner image to be fixed, at least one portion of radiation generated by at least one heat radiator of the fixer unit is not detected by the photoelectric sensor by not passing said at least one portion of the radiation generated by the at least one heat radiator through to the photoelectric sensor by use of an optical filter associated with the photoelectric sensor. An error signal is output when a fire in the fixer region is detected with the photoelectric sensor.